Compressor motor cooling arrangement for reversible refrigeration system



Oct. 31, 1961 D. J; MA COMPRESSOR MOTOR COOLING SSA 3,006,162

ARRANGEMENT FOR REVERSIBLE REFRIGERATION SYSTEM Filed Sept. 29,

INVENTOR. DON :r. MASSA HIS ATTORNEY COMPRESSOR MOTOR COLING ARRANGE-MENT FOR REVERSELE REFRIGERATION SYSTEM Don J. Massa, Louisville, Ky.,assignor to General Electrio Company, a corporation of New York FiledSept. 29, 1960, Ser. No. 59,412 4 Claims. (Cl. 62-324) The presentinvention relates to a reversible refrigeration system for an airconditioning unit adapted for heating or cooling an enclosure and moreparticularly to a reversible refrigeration system utilizing a compressorof the type commonly known as a high side case in which the highpressure discharge gas issuing from the compressor is passed into thecompressor case for cooling the motor.

It is common practice in the field of refrigeration to mount both therefrigerant compressor and its drive motor within a hermetically sealedcasing. In such an arrangement, it is necessary to devise some means forcooling the drive motor in order to maintain its temperature within safeoperating limits. One means employed for this purpose is to pass thehigh pressure discharge gas from the compressor unit over the compressormotor after this high pressure gas has been cooled to a low enoughtemperature to remove heat from the motor thereby maintaining the motorat a safe operating temperature. The heat removed from the motor iscarried by the gas into the condenser of the refrigeration system whereit is dissipated into the air stream flowing over the condenser. This isan eflicient method of maintaining the motor at a proper operatingtemperature but requires that the high pressure discharge gas beprecooled before being passed into intimate contact with the motor.

One means devised for cooling the high pressure discharge gasincorporates the injection of condensed refrigerant from some portion ofthe refrigerating system, such as from the condenser, into the hermeticcasing where it mixes with the high pressure discharge gas to cool thisgas prior to passing it over the motor. However, in order to introduceliquid refrigerant from some other portion of the refrigeration systeminto the high pressure gas stream from the compressor, it is necessaryto overcome the pressure drop which occurs in the system up to the pointfrom which the refrigerant is to be taken. An arrangement foraccomplishing this function in a nonreversible refrigeration system isdisclosed in the invention of the application of James L. Schulze,Serial No. 860,848, filed December 21, 1959, now Patent No. 2,967,410,and assigned to the assignee of the present application. The presentinvention is an improvement over the Schulze invention, which inventionwas made by the said James L. Schulze prior to the present invention.The present application does not claim anything shown or described insaid Schulze application, which is to be regarded as prior art withrespect to this present application.

A diificulty encountered when applying an injection type coolingarrangement to a reversible type refrigeration system is that thecondensed refrigerant is not always found in the same portion of thesystem. That is, during the summer when the unit is operating on thecooling cycle, the condensed liquid refrigerant is available at theoutdoor heat exchanger, while in the winter when the unit is operatingon the heating cycle to provide heat for an ice enclosure, the source ofcondensed refrigerant is at the indoor heat exchanger. Thus, in order tosupply condensed refrigerant for injection into the hermetic case, it isnecessary to devise some means for always assuring that the condensedliquid refrigerant will be available regardless of the direction ofoperation of the system.

Accordingly, it is an object of the present invention to provide animproved arrangement in a reversible refrigeration system for injectingcondensed liquid refrigerant into the hermetic casing for cooling themotor during operation of the system in either direction.

A more specific object of the present invention is to provide, in areversible refrigeration system using a capillary to expand therefrigerant from condenser pressure to evaporator pressure, an improvedinjection cooling arrangement for a compressor motor in which liquidrefrigerant utilized for injection purposes is tapped from the capillaryof the refrigeration system.

Further objects and advantages of the invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize the invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

In accordance with the present invention, there is pro vided areversible refrigeration system for an air conditioning unit adapted forheating and cooling an enclosure including a motor-compressor unitsealed within a hermetic casing and connected in reversible refrigerantflow relationship with an indoor heat exchanger and an outdoor heatexchanger. A capillary is connected between the heat exchangers forexpanding refrigerant from condenser pressure to evaporator pressure asrefrigerant flows through the system. A discharge passage leads from thecompressor into the hermetic casing for conducting high pressuredischarge gas from the compressor into the casing for cooling the motorof the unit. A portion of this discharge passage takes the form of anaspirating means, such as a venturi or jet pump, which means creates aregion of lower pressure in the high pressure gas flowing through thepassage. A liquid refrigerant conduit is connected between theaspirating means and the capillary for introduc ing liquid refrigerantfrom the capillary into the aspirating means where it mixes with thehigh pressure gas flowing through the aspirating means to cool the highpressure gas flowing through the aspirating means and thereby to coolthe compressor motor. In order to reduce the pressure .drop in thatportion of the capillary prior to its connection with the liquidrefrigerant conduit regardless of the direction of refrigerant flowthrough the system, the capillary is arranged so that the portionthereof adjacent its end communicating with the outdoor heat exchangeris in heat ex-- change relationship with the indoor heat exchanger andthat portion thereof adjacent its end communicating with the indoor heatexchanger is in heat exchange relationship with the outdoor heatexchanger so that the heat exchanger operating as an evaporator duringeither di rection of refrigerant flow through the system cools thatportion of the capillary prior to its connecting point with therefrigerant supply conduit.

For a better understanding of the invention reference may be had to theaccompanying drawing, the single FIGURE of which illustrates in somewhatschematic form a reversible refrigeration system incorporating thepresent invention.

Referring now to the drawing, there is shown a reversible cyclerefrigeration system for use in an air conditioner of the type adaptedto both heat and cool the air from an enclosure. For compressing andpumping refrigerant through the system there is provided amotorcompressor unit, generally designated by the reference numeral 2.The motor'compressor unit 2 is mounted in a hermetically sealed casing 3which houses the compressor 4 and its drive motor 6 and which issuitable for containing a high pressure refrigerant gas. A suction line7 connects directly with the suction inlet (not shown) of the compressorand carries low pressure refrigerant gas to the compressor. A dischargeline 8 is connected to the case for carrying the high pressure gas fromwithin the case into the remaining portions of the system. The dischargeline and suction line are both connected to a reversing valve 9. Alsoconnected to the reversing valve 9 are a pair of conduits 11 and 12which lead respectively to the indoor and outdoor heat exchangers orcoils 13 and 14. Included in the system for the purpose of expandingrefrigerant from condensing pressure to evaporator pressure is a firstor main capillary expansion means 16. This capillary operates as anexpansion means during both cooling and heating cycles and maintains apredetermined pressure differential between the evaporator and thecondenser regardless of the direction of refrigerant flow.

In an air conditioning unit of this type, the indoor coil 13 is arrangedfor heating or cooling air from the enclosure, while the outdoor coil 14is arranged for either rejecting heat to or extracting heat from theoutside at mosphere. The reversing valve 9 is selectively reversible todirect discharge gas into either one of the lines 11 and 12 whilereceiving low pressure gas from the other line, thereby making thesystem reversible for either heating or cooling an enclosure. Thus, ifit is desirable to set this system on the heating cycle, compressordischarge gas flowing through the discharge line 8 is connected by meansof the reversing valve 9 to the 'line 11 which carries the hot dischargegas to the indoor coil 13. This coil then acts as a condenser to give upits heat to the enclosure. If it is desired to set the system forcooling the enclosure, the suction line 7 is connected to the indoorcoil 13 through a line 1-1, which then acts as an evaporator, while thedischarge gas is carried to the outdoor coil 14 by the line 12.

During operation of the compressor, low pressure refrigerant, enteringthe compressor unit 6 from the suction line 7, is compressed within thecompressor unit to a relatively high pressure and temperature and isthen discharged by the compressor through a suitable discharge passage17, leading from the compressor discharge port (not shown) into thehermetic casing 3. For purposes of illustration, the discharge passage17 is shown as a tube leading out of the hermetic casing and then backinto the hermetic casing. However, this discharge passage could be apassage, such as that illustrated in the aforementioned Schulzeapplication, which leads from the discharge port of the compressor unitdirectly through the main frame of the unit intothe hermetic casing 6without leaving the hermetic casing. Included within the dischargepassage is an aspirating means or a venturi section, generallydesignated by the reference numeral 21, through which hot discharge gaspasses prior to entering the hermetic case. The passage 17 dischargesthe high pressure gas into the case below the motor 6 whereupon it flowsupwardly over the motor to cool the motor. The high pressure gas is thenconducted out of the casing 3 through the conduit 8 into the remainingportions of the system.

In order to cool the discharge gas flowing through the discharge passage17 sufficiently to maintain the motor 6 at a safe operating temperature,cool liquid refrigerant is withdrawn from the capillary 16 through theliquid supply conduit 26 and introduced into the high pressure gas as itflows through the aspirating means. As may be seen in the drawing, theaspirating means contains a nozzlle or gas accelerating section 22 and adiffuser or gas decelerating section 23 separated by a pinched or throatportion 24-. As the high pressure discharge gas flows through theaspirating means, it drops in pressure in the nozzle section 22 whereits velocity is increased. Then, in the diffuser section of theaspirating means, the gas pressure increases to approximately itsoriginal pressure as the velocity of the gas decreases. Thus, a pressuredrop is created in the aspirating means and a reg-ion of somewhat lowerpressure is created in the throat 2.4 of the aspirating means ascompared to the pressure of the gas discharging from the aspiratingmeans. This pressure drop in the throat 24 causes liquid or condensedrefrigerant to be siphoned through the liquid supply conduit 26 whichconnects with the capillary. The condensed refrigerant is than mixedwith the high pressure gas flowing through the discharge passage 17 andis carried by the high pressure gas into the hermetic casing 3.

Obviously, if the pressure of the refrigerant at the point the system istapped by the conduit 26 is not greater than the pressure of the gas inthe throat 24 of the venturi or aspirating means, there will be no flowof liquid refrigerant through the conduit 26. Normally the pressure inthe throat 24 is less than the latter stages of the heat exchangeroperating as a condenser. However, the restriction in the early stagesof the capillary must be reduced as much as possible in order to preventthe prwsure of the refrigerant at the conecting point 26a of the conduit26 and the capillary from dropping below that in the throat 24 of theventuri.

In order to reduce the pressure drop in that portion of a capillary 16prior to its connecting point 26a with the refrigerant supply conduit26, the capillary is arranged so that the portion thereof ahead of theconnecting point with the refrigerant supply conduit 26 is always cooledby the heat exchanger operating as an evaporator. Referring now to thedrawing, it can be seen that the portion 16a of the capillary adjacentthe end 16b, which communicates with the outdoor heat exchanger 14, isdisposed within the indoor heat exchanger 13. That is, the portion 16aof the capillary is in heat exchange relationship with the heatexchanger 13 and is influenced by the temperature of that heatexchanger. Similarly, the portion 16c of the capillary adjacent the end16d, which communicates with the indoor heat exchanger, is disposedwithin the outdoor heat exchanger 14. That is, that portion of thecapillary is in heat exchange relationship with the outdoor heatexchanger 14 and is influenced by the temperature of that heatexchanger. Thus, it will be seen that, regardless of the direction offlow of the refrigerant, the heat exchanger operating as an evaporatoralways cools that portion of the capillary ahead of the connecting point26a between the capillary and the conduit 26. When the system isoperating on the cooling cycle and the indoor heat exchanger 13 is theevaporator, refrigerant flow through the system is from the condenser 14through the end 16b of the capillary 16 into that portion 16a of thecapillary which is in heat exchange relationship with the heat exchanger13 acting as an evaporator. On the cooling cycle refrigerant flowsthrough portion 16a of the capillary prior to reaching the connectingpoint 26a of the conduit 26. On the heating cycle, the refrigerant flowthrough the system is from the heat exchanger 13, which is thenoperating as a condenser, through the end 16d of the capillary into thatportion 160 of the capillary in heat exchange relationship with the heatexchanger 14, then operating as an evaporator. Thus, during the heatingcycle, the portion 160 of the capillary is in heat exchange relationshipwith the evaporator of the system or heat exchanger 14, and that portion166 of the capillary is cooled prior to the connecting point 26a of therefrigerant supply conduit 2 By cooling that portion of the capillaryjust prior to the connection 26a between the capillary and the conduit26 the refrigerant in that portion of the capillary is maintained inliquid form and flows rapidly through the capillary with very littlepressure drop.

However, it will be noted that the portion of the capillary after theconnecting point 26a with the refrigerant supply conduit 26 is always inheat exchange relationship with the condenser of the system. Thisportion of the capillary, therefore, is heated by the condenser andcauses the refrigerant flowing therethrough to become vaporous therebygreatly increasing the restriction in that portion of the capillary. Bythis arrangement, therefore, most of pressure drop in the capillary isexperienced in that portion of the capillary after the connecting pointwith the refrigerant supply conduit 26 regardless of the direction ofrefrigerant flow through the system and the pressure drop in thatportion of the capillary prior to the connecting point 26a with theconduit 26 is slight. By keeping the pressure drop in the portion of thecapillary prior to its connecting point with the conduit 26 as small aspossible, the pressure of the refrigerant at the connecting point 26a isgreater than the pressure in the throat 24 of the aspirating means andliquid refrigerant consequently flows through the conduit 26 into theaspirating means. The condensed refrigerant then mixes with the highpressure gas flowing through the discharge passage 17 and is carried bythe high pressure gas into the hermetic casing 3 to cool the motor 6.When liquid refrigerant is introduced into the throat or low pressureregion of the aspirating means, it encounters the hot discharge gas andis vaporized or flashed into gaseous form. Heat removed from thedischarge gas in vaporizing the liquid refrigerant reduces thetemperature of the discharge gas and the violent reaction created by theflashing of the liquid into vaporized form completely mixes the gas sothat the resultant gas mixture issuing from the passage is at a uniformtemperature and much cooler than the temperature of the original highpressure gas discharge from the compressor.

It is sometimes desirable to include a restricting means or secondcapillary 31 in the conduit 26 as illustrated in the drawing. The designof the restricting means or second capillary 31 should permit enoughcondensed refrigerant to flow through the conduit 26 to suflicientlycool the discharge gas but still limit the flow sufl'iciently toeliminate short circuiting of the evaporator and eventual collection ofthe refrigerant in liquid form within the case. Obviously a capillarydoes not have to be used for this purpose. Other means such as a needlevalve or other type of restriction could easily be substituted for acapillary.

In operation, the venturi section or aspirating means 21 acts as amodulating device for supplying greater or lesser amounts of condensedrefrigerant to cool the high pressure discharge gas according to theflow of gas through the discharge passage in the condenser unit. Sincethe amount of liquid refrigerant flowing through the supply conduit 26depends to a great extent upon the pressure recovery experienced in thediffuser section 23 from the throat 24 to the outlet of the diffuserand, since the amount of pressure recovery in the venturi or aspiratingmeans is a function of the quantity of gas flowing therethrough, it isapparent that the amount of liquid refrigerant siphoned from the liquidrefrigerant supply conduit 26 depends upon the quantity of discharge gasflowing through the discharge passage -17 leading from the compressorunit. Whenever the pressure of the suction gas is high, the temperatureof the gas at the discharge outlet of the compressor 6 is, under normalconditions, relatively high and its cooling requirement is, therefore,substantial. It is well known, however, that when the suction pressureis high, a correspondingly greater quantity of gas is pumped and thisresults in a greater flow of liquid refrigerant through the passage 17and through the throat 24- thereby increasing the flow of liquidrefrigerant through the conduit 26 and supplying the necessary coolingof the high pressure discharge gas. Conversely, when the suctionpressure is low and the compressed discharge gas is at a relatively lowtemperature, the amount of gas being pumped through the dischargepassage 17' is correspondingly less. This, consequently, produces acorrespondingly smaller pressure difference between the throat 24 andthe outlet of the aspirating means thereby resulting in a diminishedflow through the conduit 26 and a lesser amount of cooling of thedischarge gas. Thus, under most conditions, of operation, the aspiratingmeans automatically modulates the amount of cooling of the discharge gasfrom the compressor, and automatically increases or decreases thecooling effect on this gas to maintain the motor within safe operatinglimits.

It will be noted that the connecting point 26a between the conduit 26and the capillary 16 is more toward the indoor heat exchanger side ofthe capillary than toward the outdoor portion of the capillary. It hasbeen found desirable to provide as little of the capillary as possiblebetween the connecting point 26a of the conduit 26 and the cooledportion 16a of the capillary during the cooling cycle so that the amountof pressure drop in that portion of the capillary is held to a minimumon the cooling cycle operation. On the heating cycle this factor is notas critical since the amount of liquid refrigerant required for motorcooling purposes is normally less. Also, in this arrangement, thatportion of the capillary adjacent the outdoor heat exchanger isgenerally exposed to outdoor air which, during the heating cycle, isusually fairly cold and, thus, serves to cool that portion of thecapillary between the outdoor heat exchanger 14 and the connecting point26a and to reduce the pressure drop therein.

By the present invention there has been provided in a reversiblerefrigeration system a siphoning arrangement for injecting liquidrefrigerant into the hermetic casing of a motor-compressor unit formotor cooling purposes regardless of the direction of refrigerant flowthrough the system. Moreover, this arrangement taps liquid refrigerantfrom the capillary of the system and provides an arrangement whereby thepressure drop in the capillary up to the tapping point is maintainedrelatively small regardless of the direction of refrigerant flow throughthe system thereby assuring flow of liquid refrigerant from thecapillary into the siphoning means.

While in accordance with the patent statutes there has been describedwhat at present is considered to be the preferred embodiment of theinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made therein without departing frornthe invention, and it is, therefore, the aim of the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

What I claim as new and desire to secure by letters Patent of the UnitedStates is:

1. A reversible refrigeration system for an air conditioning unitadapted for heating and cooling an enclosure comprising amotor-compressor unit, an indoor heat exchanger and an outdoor heatexchanger connected in reversible refrigerant flow relationship, meansfor reversing the flow of refrigerant through said system thereby tooperate each of said heat exchangers interchangeably as a condenser oras an evaporator, a hermetic casing surrounding said motor-compressorunit for containing a high pressure refrigerant gas, a discharge passageleading from said compressor of said unit into said hermetic casing forconducting compressed refrigerant gas into said casing for cooling saidmotor, said discharge passage including an aspirating means for creatinga low pressure region in said discharge gas as said gas passes throughsaid aspirating means, a capillary having one end thereof communicatingwith said indoor heat exchanger and the other end thereof communicatingwith said outdoor heat exchanger for expanding refrigerant fromcondenser prescapillary adjacent said other end of said capillarycommunicating with said outdoor heat exchanger being in heat exchangerelationship with said indoor heat exchanger and a portion of saidcapillary adjacent said one end of said capillary communicating withsaid indoor heat exchanger being in heat exchange relationship with saidoutdoor heat exchanger, and a liquid refrigerant supply conduit havingone end connecting with said capillary at a point between said portionsthereof in heat exchange relationship with said heat exchangers, saidconduit connecting at its other end with said aspirating means forconducting liquid refrigerant from said capillary into said low pressureregion of said aspirating means where it mixes with and cools saiddischarge gas in said passage prior to entering said hermetic case, saidheat exchanger operating as an evaporator during either direction ofrefrigerant flow through said system coo-ling that portion of saidcapillary prior to its connecting point with said refrigerant supplyconduit so that there is little pressure drop in that portion of saidcapillary prior to said connecting point with said refrigerant supplyconduit as compared to the pressure drop in that portion of saidcapillary after said connecting point with said refrigerant supply condut.

2. A reversible refrigeration system for an air conditioning unitadapted for heating and cooling an enclosure comprising amotor-compressor unit, an indoor heat exchanger and an outdoor heatexchanger connected in reversible refrigerant flow relationship, meansfor reversing the flow of refrigerant through said system thereby tooperate each of said heat exchangers interchangeably as a condenser oras an evaporator, a hermetic casing surrounding said motor-cornpressorunit for containing a high pressure refrigerant gas, a discharge passageleading from said compressor of said unit into said hermetic casing forconducting compressed refrigerant into said casing for cooling saidmotor, said discharge passage including a venturi for creating a lowpressure region in said discharge gas as said gas passes through saidventuri, a cap .illary having one end thereof communicating with saidindoor heat exchanger and the other end thereof communicating with saidoutdoor heat exchanger for expanding refrigerant from condenser pressureto evaporator pressure during either direction of refrigerant flowthrough said system, a portion of said capillary adjacent said one endof said capillary communicating with said indoor heat exchanger being inheat exchange relation- ,ship with said outdoor heat exchanger and aportion of said capillary adjacent to said other end of said capillarycommunicating with said outdoor heat exchanger being in heat exchangerelationship with said indoor heat exchanger, and a refrigerant supplyconduit connected at one end to said venturi and connecting at the otherend with said capillary at a point between said portions of saidcapillary in heat exchange relationship with said heat exchangers, saidconduit adapted to conduct liquid refrigerant from said capillary intosaid venturi for mixing with and cooling said discharge gas flowingtherethrough, said heat exchanger operating as an evaporator duringeither direction of flow through said system cooling that portion ofsaid capillary prior to its connecting point with said refrigerantsupply conduit so that there is little pressure drop in that portion ofsaid capillary prior to said connecting point with said refrigerantsupply conduit as compared to the pressure drop in that portion of thecapillary after said connecting point with said refrigerant supplyconduit.

3. A reversible refrigeration system for an air conditioning unitadapted for heating and cooling an enclosure comprising amotor-compressor unit, an indoor heat exchanger and an outdoor heatexchanger connected in reversible refrigerant flow relationship, meansfor reyersing the flow of refrigerant through said system thereby 'tooperate each of said heat exchangers interchangeably 'as a condenser oras an evaporator, a hermetic casing surrounding said motor-compressorunit for containinga high pressure refrigerant gas, a discharge passageleading from said compressor of said unit into said hermetic casing forconducting compressed refrigerant gas into said casing for cooling saidmotor, said discharge passage including a venturi for creating a lowpressure region in said discharge gas as said gas passes through saidventuri, a capillary communicating at one end with said indoor heatexchanger and communicating at the other end with said outdoor heatexchanger for expanding refrigerant from condenser pressure toevaporator pressure, a portion of said capillary adjacent said one endthereof communicating with said indoor heat exchanger being in heatexchange relationship with said outdoor heat exchanger and a portion ofsaid capillary adjacent said other end thereof communicating with saidoutdoor heat exchanger being in heat exchange relationship with theindoor heat exchanger, a refrigerant supply conduit connecting at oneend to said venturi and connecting at the other end thereof with saidcapillary at a point between said portions of said capillary in heatexchange relationship with said heat exchangers for conducting liquidrefrigerant from said capillary into said venturi, said conduitconnecting with said capillary at a point closer to said indoor heatexchanger than to said outdoor heat exchanger, said heat exchangeroperating as an evaporator during either direction of refrigerant flowthrough said system cooling that portion of said capillary prior to itsconnecting point with said refrigerant supply conduit so that there islittle pressure drop in that portion of said capillary prior to saidconnection point with said refrigerant supply conduit as compared to thepressure drop in that portion of said capillary after connecting pointWith said refrigerant supply conduit.

4. A reversible refrigeration system for an air conditioning unitadapted for heating and cooling an enclosure comprising amotor-compressor unit, an indoor heat exchanger and an outdoor heatexchanger connected in reversible refrigerant flow relationship, meansfor reversing the flow of refrigerant through said system thereby tooperate each of said heat exchangers interchangeably as a condenser oras an evaporator, a hermetic casing surrounding said motor-compressorunit for containing a high pressure refrigerant gas, a discharge passageleading from said compressor of said unit into said hermetic casing forconducting compressed refrigerant gas into said casing to cool saidmotor, said discharge passage including an aspirating means for creatinga low pressure region in said discharge gas as said gas passes throughsaid aspirating means, a first capillary having one end thereofcommunicating with said indoor heat exchanger and the other end thereofcommunicating with said outdoor heat exsure to evaporator pressureduring either direction of refrigerant flow through said system, aportion of said first capillary adjacent said other end of saidcapillary communicating with said outdoor heat exchanger being in heatexchange relationship with said indoor heat exchanger and a portion ofsaid first capillary adjacent said one end of said capillarycommunicating with said indoor heat exchanger being in heat exchangerelationship with said outdoor heat exchanger, a refrigerant supplyconduit connecting at one end with said low pressure region in saidaspirating means and having its other end connecting with said firstcapillary at a point between said portions thereof in heat exchangerelationship with said heat exchangers, said refrigerant supply conduitadapted to conduct liquid refrigerant from said first capillary intosaid low pressure region of said aspirating means where it mixes withand cools said discharge gas in said passage prior to entering saidhermetic casing, a second capillary in said refrigerant supply conduitfor restricting flow through said refrigerant supply conduit andpreventing short circuiting of said refrigerant around said heatexchanger operating as an evaporator, said heat exchanger operating asan evaporator during either direction of refrigerant flow through saidsystem cooling that portion of said first capillary prior to itsconnecting point with said refrigerant supply conduit so that there islittle pressure drop in that portion of said first capillary prior tosaid connecting point with said refrigerant supply conduit as comparedto the pressure drop in that portion of said first capillary after saidconnection with said refrigerant supply conduit.

References Cited in the file of this patent UNITED STATES PATENTS

